The present invention relates to a composite sliding member used in all kinds of industries, and more particularly to a composite sliding member consisting of a steel backing and a high quality lining of copper-lead alloy or lead-bronze alloy which is formed readily and economically on the steel backing by the plasma arc build up welding method and, to a producing method of the composite sliding member.
Conventional composite sliding members consisting of copper-lead alloy or lead-bronze alloy layer are usually produced by melting and casting those alloys. The conventional method requires a number of processes including casting, and thus are costly.
Alternatively, according to other methods, a copper alloy layer is formed on a steel backing by cladding according to the metal spraying method or the various kinds of build up welding method (TIG welding, arc welding, gas welding, etc.). Those methods have been applied only to produce alloys containing no lead, such as aluminum-bronze, phosphorous bronze and brass except for lead-containing alloys which exhibit superior friction properties. The reasons, why the metal spraying and the build up methods are not in general applied to lead-containing alloys, are that harmful lead evaporation is generated during the metal spraying process or the welding process, the yield of lead is low and the lead segregates to an extreme degree in the alloy. Thus, the cladding method of metal spraying or build up welding is applied to the copper alloys with no lead, such as aluminum-bronze, phosphorous bronze and brass.
The method of producing composite sliding members by means of the casting process requires the dangerous and hard work at a high temperature. Because the melting temperature of copper-lead alloy and lead-bronze alloy, in particular, is above 1000.degree. C., harmful lead fumes are generated so that the working environment is very poor. Controlling of casting condition is difficult which requires the experience of skilled workers.
Excluding the products with lining on an inner surface of a backing metal by means of the centrifugal casting process, the set up of a stopper (or a weir) for molten metal is required in case of gravity casting on a thrust face or for lining of the outer surface of the backing metal in order to prevent molten metal from flowing out from the backing metal, so the preparations for casting require great expense.
In order to produce normal castings without a blow hole by means of casting, a riser with a height of several times as large as a thickness of a product lining is required, which causes a reduction in the yield and increases production cost.
In case of casting on a surface of a housing with a complicated form, a non-uniform structure and segregation of the cast alloy, or a poor bonding to the housing are apt to occur due to non-uniform cooling.
According to casting processes, even in the case where a lining is required on a mere small part of a product, the entire backing metal in must be provided with a lining and then the mostly unnecessary part thereof must be cut off, resulting in the low yield which is not economical.
On the other hand, the methods of producing composite sliding members by means of metal spraying or the welding are free from the high-temperature work involved in casting, and relatively easy methods for cladding by build up welding of high melting point metals. However, the metal spraying or the welding of lead-containing alloys exhibiting excellent friction property, is very harmful because of the evaporation of the lead at the metal spraying or welding process. Further, according to those processes, the yield of lead is so low that objective compositions cannot be obtained, and a uniform and fine structure cannot be produced due to much lead segregations. Thus, the properties of composite sliding members, which are required to have a high speed and a greater specific load, cannot be improved.